24v Growatt or MPP Wiring Diagram with a few questions

[Wildman13]

Hello Everyone,
I have researched several other posts here as well as a good bit of video (Will Prowse) and come up with the following system AND a few questions that I couldn't find answers to or my brain couldn't process (possible information overload). My wife and I just sold our current RV and travel to California in a few weeks to get our new one and have to put solar in first thing as we are full timers and need POWER! lol

MPP or Growatt 24V 3k all in one

Question 1 - Mounting of All in one
A. Can these be mounted inside the storage compartment of an RV? I've seen people use a metal backing due the instructions mentioning heat.Putting a piece of metal on the carpet interior seems like it would just transfer the heat? Also I imagine the inside of an RV storage compartment ca get pretty hot. Is there an operating temperature to worry about?
B. Can they be mounted sideways?
I am looking at putting on two large panels, 390 watts each, wired in parallel for shade issues.

Question 2 - PV Breaker / All in one inputs
I was told with just the two panels I didn't need one. Do I a breaker and if so what specs? Also do I need a breaker due to there only being 1 input on the All in one systems or is there a part that combines the 2 wires down to 1 and if so what's that "technically called"

Question 3 - Can someone recommend tall brackets that will mount those solar panels on top of the RV with room to clear the vents fans and skylights?

I'm looking to run TWO SoK 206ah Lithium batteries (or equivalent) in series to make 24v

Question 4 - What Size accessories do I need
Battery Fuse size? I think a 300amp
Busbar size? I have no clue tbh. is there an equation or reference for this?
24V to 12V Buck step down? Is 40amps enough, not sure how this is figured

Wiring Diagram
I basically took someone else similar one off of this webpage. I'm trying not to ask the same questions everyone has every week.
A. Does it look correct?
B. If I added a battery monitor with shunt where does that go in the diagram? On my current set up it's just off the negative busbar (see picture)

Thanks in advance and sorry as I'm sure I've asked questions already asked before

 

[HRTKD]

Speaking generically, since I don't have a Growatt...

Creating a mounting system that allows the device to stay cool is critical. Mounting it in such a way that the device overheats is not a good way to start. Perhaps a bracket that allows the device to stand off/away from the wall will be all you need. If the device is passively cooled (fins) then it has to be mounted with the fins going vertical. If it uses fans to cool then a horizontal orientation may be allowed. It all depends on what your owner's manual says.

A breaker between the PV and the solar charge controller is highly recommended. The breaker makes it easy to disconnect the PV input should you need to work on the rest of the system. If you put more than 2 panels in parallel then you will need to use a fuse between each parallel panel/string. The breaker is sized to be slightly larger than the maximum amperage output of the panels. Two panels in parallel is twice the amps of a single panel. The usual fudge factor is 1.25. If your combined panels put out 10 amps then you need a minimum of a 12.5 amp breaker. Round up, not down, so probably a 15 amp breaker. Be sure you use actual PV rated wire coming off of the panels and going into the RV.

I would not recommend locating panels over other objects on the roof. If you have to put panels over objects already on the roof then you should look at different panels that fit better.

My preference is to not put LiFePO4 batteries in series. If you need 24v, then buy a 24v battery.

The fuse immediately downstream of the battery is sized for your loads. If you're going to draw 200 amps (a huge amount on a 24v RV system) then you need a fuse that is larger than 200 amps. Your wiring and common bus bars must also support the number of amps that you'll draw.

You need an energy audit to know how many amps the 12v side of the system draws.

The shunt for a battery monitor will go immediately downstream of the battery, usually on the negative side. Nothing else gets connected to the battery except for temperature probes.

You didn't ask about wires. This is just as critical as fuses. To figure out the proper wire size you need to know amps, volts and distance. Plug those into a wire gauge calculator and you'll know for sure what size wire to use. I use the calculator linked below.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

 

[Wildman13]

Speaking generically, since I don't have a Growatt...

Creating a mounting system that allows the device to stay cool is critical. Mounting it in such a way that the device overheats is not a good way to start. Perhaps a bracket that allows the device to stand off/away from the wall will be all you need. If the device is passively cooled (fins) then it has to be mounted with the fins going vertical. If it uses fans to cool then a horizontal orientation may be allowed. It all depends on what your owner's manual says.

A breaker between the PV and the solar charge controller is highly recommended. The breaker makes it easy to disconnect the PV input should you need to work on the rest of the system. If you put more than 2 panels in parallel then you will need to use a fuse between each parallel panel/string. The breaker is sized to be slightly larger than the maximum amperage output of the panels. Two panels in parallel is twice the amps of a single panel. The usual fudge factor is 1.25. If your combined panels put out 10 amps then you need a minimum of a 12.5 amp breaker. Round up, not down, so probably a 15 amp breaker. Be sure you use actual PV rated wire coming off of the panels and going into the RV.

I would not recommend locating panels over other objects on the roof. If you have to put panels over objects already on the roof then you should look at different panels that fit better.

My preference is to not put LiFePO4 batteries in series. If you need 24v, then buy a 24v battery.

The fuse immediately downstream of the battery is sized for your loads. If you're going to draw 200 amps (a huge amount on a 24v RV system) then you need a fuse that is larger than 200 amps. Your wiring and common bus bars must also support the number of amps that you'll draw.

You need an energy audit to know how many amps the 12v side of the system draws.

The shunt for a battery monitor will go immediately downstream of the battery, usually on the negative side. Nothing else gets connected to the battery except for temperature probes.

You didn't ask about wires. This is just as critical as fuses. To figure out the proper wire size you need to know amps, volts and distance. Plug those into a wire gauge calculator and you'll know for sure what size wire to use. I use the calculator linked below.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

Thank you for your response.

I've tried to answer all your points. Please let me know if my answers are correct or what I am missing.

- For the PV breaker I am looking at each panel being around 10amps, I might add panels later and breakers are cheap so a 50amp breaker would cover 4 panels. 10x4=40 x 1.25 = 50

- on the wire, we used 8GA wire on my current rig (my buddy was the lead) I don't think it was PV but thats good to know.

- For the fuse downstream of the battery and the busbars I will be running TWO 12v SoK 206ah batteries in series. They are designed for series. I checked after you comment. They each have a 100amp max discharge (BMS). When I am running small appliances they will be pulling up to 1800 watts which is 150 amps at 12v (not sure if thats's half at 24v as I am new to the 24v stuff). I would imagine a 200 or 250 amp fuse and busbars at 12v. is it half for 24v?

I have not done an energy audit for the new rig. We did one on our current rig with 600 watts of panels and 220ah lead acid. We use 15%-30% per day (per our battery monitor). In our new rig the difference will be using a ninja air fryer for 30-60 minutes per day which has a consumption of 1450 watts so that will pull a lot (60-120amp hours per my math) Our new battery bank is 412ah at 12v which is 4x what we have available now. We'll then have 740-780 watts of solar so I think this system is pretty well balanced for our uses.

Please correct me if I'm wrong.

Thanks,

Lee

 

[HRTKD]

- For the PV breaker I am looking at each panel being around 10amps, I might add panels later and breakers are cheap so a 50amp breaker would cover 4 panels. 10x4=40 x 1.25 = 50

How are you going to wire your panels? In series or parallel? If you do series then 50 amp is too high.

Wired in series: volts increase, amps stay the same
Wired in parallel: volts stay the same, amps increase.

- For the fuse downstream of the battery and the busbars I will be running TWO 12v SoK 206ah batteries in series. They are designed for series. I checked after you comment. They each have a 100amp max discharge (BMS). When I am running small appliances they will be pulling up to 1800 watts which is 150 amps at 12v (not sure if thats's half at 24v as I am new to the 24v stuff). I would imagine a 200 or 250 amp fuse and busbars at 12v. is it half for 24v?

Two 100 amp discharge batteries wired in series, is still only 100 amps. 1800 watts / 24 volts / .85 inverter efficiency = 88 amps. You should be OK, but 88 amps isn't far from 100 amps. I don't know the reputation of SoK and if their BMS can handle the continuous rating for long. Don't forget that some devices have a surge that can exceed the normal rating.

250 amp @ 12v is a common rating for bus bars.

I have not done an energy audit for the new rig. We did one on our current rig with 600 watts of panels and 220ah lead acid. We use 15%-30% per day (per our battery monitor). In our new rig the difference will be using a ninja air fryer for 30-60 minutes per day which has a consumption of 1450 watts so that will pull a lot (60-120amp hours per my math) Our new battery bank is 412ah at 12v which is 4x what we have available now. We'll then have 740-780 watts of solar so I think this system is pretty well balanced for our uses.

It helps to have experience with an existing system. It sound like you are going into this with that experience.

 

[Wildman13]

How are you going to wire your panels? In series or parallel? If you do series then 50 amp is too high.

Wired in series: volts increase, amps stay the same
Wired in parallel: volts stay the same, amps increase.

I was going to wire the 2 in parallel in case 1 was shaded. Thats why I planned for the fuse at 50amp if I added 2 in the future. Should I just get a fuse for the 2 now so a 25amp then upgrade a new fuse "if"I add more panels? they are cheap so no biggie

Two 100 amp discharge batteries wired in series, is still only 100 amps. 1800 watts / 24 volts / .85 inverter efficiency = 88 amps. You should be OK, but 88 amps isn't far from 100 amps. I don't know the reputation of SoK and if their BMS can handle the continuous rating for long. Don't forget that some devices have a surge that can exceed the normal rating.

yeah I was still doing 12v math and doubling the BMS, either way i'm good. Thanks fro getting me back on 24v. The SoK are very well liked and rated. @Will Prowse loves these things which is where I found them

250 amp @ 12v is a common rating for bus bars.



It helps to have experience with an existing system. It sound like you are going into this with that experience.

So I guess I need to do 24v math here as well. so at 24v I would just need Fuse and busbars rated at 100 or 125 amps it appears.

Am I back on track now? lol

 

[HRTKD]

It's easier and less expensive to wire the panels in series. You do need to verify that the panel Voc x 2 doesn't exceed the Maximum PV Input Voltage of the Growatt.

I have two panels on the roof of my RV, wired in series. I figure if one is in the shade, the other one probably will be also. I have two ground deployable panels that I can put out if the roof is shaded. I do mostly boondocking, so I pick where I camp based on shade, as in no shade.

 

[Wildman13]

It's easier and less expensive to wire the panels in series. You do need to verify that the panel Voc x 2 doesn't exceed the Maximum PV Input Voltage of the Growatt.

I have two panels on the roof of my RV, wired in series. I figure if one is in the shade, the other one probably will be also. I have two ground deployable panels that I can put out if the roof is shaded. I do mostly boondocking, so I pick where I camp based on shade, as in no shade.

The panels VoC is 48 - 53 (depending on which one I go with and the MPP (Growatt out of stock) is 145VDC. So I could put 2 in series but be capped there, meaning adding a 3rd would require a re-wire. We will be doing mostly boondocking as well but we like to go exploring and there are lot of places with shade and any power is better than no power. We will have a 2500 watt genny as back up

 

[HRTKD]

Odd numbers of panels can be challenging for configurations. Even numbers tend to work out better.

 

[Wildman13]

Look like I'm down to wire size.

Solar panel wires
I used the calculator and came up with only needing small cable due to 24v.

2 Panels putting out about 9 amps each, (parallel)
*I can wire in series just not sure what benefit it would 'really be" on this size system. Go with slightly smaller wire?

15' max run
24v

I used 8awg in my current 12v system. Probably go with the same.

Battery wires
using the same calculator i once again came up with a much smaller # than I currently have on my 12v system

I used max amps of 100 (most likely be around 65amps)
5' run
24v

It says I can use 6awg which is crazy small (in my mind anyways) Most likely use 2awg

Did I get all that right? The 24v is a game changer it appears

 

[HRTKD]

I think you're using the wrong numbers for your PV wire. The voltage is going to be 96v or 106v if you wire in series, 48v or 53v if in parallel. You don't get 24v until AFTER the solar charge controller.
96v, 15' (30' round trip), 9 amps: 14 gauge PV cable (14 gauge is the smallest PV wire I'm familiar with. I wouldn't go lower)
48v, 15' (30' round trip), 18 amps: 14 gauge PV cable (2.96% voltage drop, still OK, but 12 or 10 would be better)

10 gauge is the biggest PV cable that fits the commonly found MC4 connectors. When you drop to 8 gauge, the selection of MC4 connectors drops off significantly. If you have 8 gauge PV wire already, might as well use it.

I get the same 6 gauge for the battery. I would go bigger also. I'm using 2/0 on each of my 120 amp 12v batteries.

 

[Wildman13]

Well we just used 8awg wire last time, not PV so maybe that's it. I don't have any left over going to order it all

 

[HRTKD]

Whatever PV wire you buy, it should be UL 4703 certified. I used 10 gauge for my two 320 watt panels wired in series, over about 15' (one-way) distance. Bigger than necessary, but very little voltage drop.